Sun Return Mission
Reaching the Sun and returning is probably the most difficult task one can do in this simulator. Land & Return To land on the Sun and return home is actually possible only in sandbox mode, because of the following problems: *Solar gravity is too strong even for the most powerful engines, which cannot lift the smallest required cargo (a 2.5 t fuel tank and a probe). *Solar atmosphere will slow down any ship attempting to reach escape velocity. *The amount of fuel needed is too large, even if, somehow, a better engine will be developed. *There is no solid surface on the Sun. So, if you try to land, you will reach altitude zero and continue to go down. Still, in sandbox mode, with no gravity, no atmosphere drag and unlimited fuel, it is possible to reach altitude zero and make it back home. Sun Grazing & Return Using a huge amount of fuel, it is possible to send a ship very close to the Sun, then return to Earth. The ship will not actually land, but will get as close as possible to the Sun. The main problem, as can be seen on the Delta-v chart, is that, reaching the Sun will require 30000 delta-v units. Compared, this is about 10 times more then the delta-v budget required to reach Mercury or Venus. The mission will also require to store the needed fuel for return, which in turn, will require far more fuel for getting to the Sun. The Ship The needed amount of fuel is far beyond what can be carried by a single ship. It will require at least 10 launches (and probably even more), consisting mainly of fuel tanks, ion engines and sources of electricity. Then, all parts need to be assembled into a single, giant ship. The ship listed on top-right of this page is in low Sun orbit. It was 3 times larger when it left low Earth orbit and when it returned to Earth, it had only 7 t of fuel left. It required 14 independent launches for bringing the parts, plus many others for fuel supply. The Ion Engine is probably the only way of propulsion for such a mission. Using chemical engines will require a ship many times larger. The Solar Panel is not the best source of energy, because there is not enough room on the ship for all panels needed, except for the last stages. The RTG is a better option. When transferring fuel from one tank to another, the orbit will be slightly changed. Also, the many docking processes will change the orbit. In order to avoid getting too low, it is good to start assembling the ship at a higher altitude, like 40 km. Leaving Earth Ion engines don't have the same thrust as chemical engines. At least at the beginning, the ship will spiral away from Earth until it will escape its sphere of influence. Even with all the fuel stored onboard, it is very important to preserve as much as possible. Lowering Periapsis A long, continuous engine burn, will lower the periapsis down to the Sun. This can be started from Earth's distance, but it will be more efficient if started from further away, beyond Mars because of the Oberth Effect. If the ship uses multiple flybys to get closer to the Sun (like from Mercury), the needed amount of fuel will be much higher, depending on the fuel needed for encounter maneuvers. The Parker Solar Probe used this method to go closer to the Sun, but because of the fuel and time needed for encounters, the probe will be at its lowest at around late 2020 or 2030. Lowering Apoapsis Below 1000 km, the Sun's corona has a very small Aerobrake effect. However, this effect is too little and it also rises the periapsis. Sun's atmosphere starts at 300 km. Solar atmosphere has a very powerful braking effect and must be used with care. Setting the periapsis at 299.7 to 299.9 km will be good enough to lower the apoapsis. Setting the periapsis below 299.0 km will slow the ship too much, making it unable to escape. Solar aerobrake is impossible for versions older than 1.3, because those versions don't display apoapsis and periapsis data. Each aerobrake will also slightly rise periapsis, requiring small engine burns to correct trajectory. Closing In Below the altitude of 3000 km, aerobrake becomes risky. It is better to use the engines and slowly spiral towards the Sun. A ship can lower its orbit down to 300 km. Beyond this value, it will enter Sun's atmosphere, which will slow it down too much. However, influences from the corona will alter the orbit. Because of this, it is better to fix a higher orbit, for example at 310 km. Once the ship is at 310 km, it is good to move fuel from a tank to another, to dump empty tanks and to deploy a probe, that will remain in orbit. Returning From low Sun orbit, a ship needs to use tremendous amounts of fuel, to return. It is good, at first, to use the engines continuously, to spiral to a higher, safe altitude (for example 1000 km, to avoid perturbations from the corona). From this altitude, in order to save some fuel, the ship will fire its engines only around periapsis, to gradually rise its apoapsis. The process requires huge amounts of time and fuel. From time to time, the pilot will need to adjust ship's inclination and to dump empty fuel containers. Returning will require the highest amount of fuel. Passing Mercury Orbit Once a ship has passed Mercury's orbit, it will be possible to use multiple Mercury and Venus flybys to get to Earth. Unfortunately, this will take much time, it will at first only rise the periapsis and will not save much fuel. The delta-V budget needed to reach from low Sun orbit to Mercury's orbit is high, probably 20 times higher then the delta-V budget needed to reach from Mercury's orbit to the Earth. So, it makes more sense, once a ship crossed Mercury's orbit, to continue burning until it crosses Earth's orbit. Reaching Earth from the Sun is challenging. First of all, the ship will approach on a highly elliptical orbit, moving very fast compared to the Earth. Secondly, while coming from the Sun, the orbital path will not be very precise. The ship will approach very fast and might not be slowed enough from Earth's atmosphere. It is, therefore, very important to conduct Trajectory Correction Maneuvers before reaching Earth. The ship must go through Earth's atmosphere, very close to the surface, but not on an impact trajectory with the surface. The atmosphere should slow a ship enough to safely land. Achievements There are no official Achievements for this type of mission. Still, it can offer much satisfaction, as the Sun is the most difficult object to reach in the Solar System. Category:Gameplay